This invention pertains to optical communications systems, in general, and to interferometers used in communications systems, in particular.
An optical cross-connect device is functionally a four port device that works with optical signals comprising a plurality of different wavelengths. An optical cross-connect has an input port, a through port, an add port, and a drop port. Multiplexed wavelength optical signals at the input port are coupled to the through port. The use of add and drop ports allow optical signals at specific wavelengths to be xe2x80x9caddedxe2x80x9d in place of the corresponding wavelength optical signals in the input port signals that in turn are switched to the drop port. This enables optical wavelength components signals to be added and dropped to/from multiplexed wavelength optical signals. An ideal optical cross-connect device is capable of dropping any combination of wavelengths from the input port to the drop port and adding any wavelengths combinations from an add port to the through port.
Wavelength routing optical cross-connect arrangements presently available separate incoming wavelengths received at inputs by utilizing DWDM demultiplexing. Typically large-scale optical switch matrices are utilized to switch and route the de-multiplexed single wavelength signals. In one arrangement micro-machined mirrors are utilized in what is referred to as MEM technology. In other arrangements, total internal reflection techniques are utilized with bubble or liquid crystal displays. These prior arrangements combine out-going wavelengths using DWDM multiplexers.
Optical switch matrices based on wavelength routing optical cross-connects have severe limitations. To provide for switching of multiplexed optical signals having xe2x80x9cnxe2x80x9d wavelengths, a complex nxc3x97n optical switch matrix must be utilized. Where xe2x80x9cnxe2x80x9d is a large number, the size of the matrix becomes very large and the cost to provide such a matrix is high. In addition, the insertion loss is also very highxe2x80x94typically in excess of 10 dB for a 64 wavelength optical cross-connect. Because the size of the matrix increases in accordance with the square of xe2x80x9cnxe2x80x9d it is also difficult to scale up for a matrix to handles larger numbers of wavelength channels. To provide a 256 wavelength optical cross-connect requires over 64,000 switching elements. In addition, such matrices typically operate at a relatively slow speed, on the order of 10 milliseconds. The slow speed is a result of utilizing some sort of mechanical movement. The mechanical movement itself leads to reliability issues.
In accordance with the principles of the invention, optical apparatus for selectively coupling optical wavelength components of wavelength multiplexed signals comprising wavelength components each at a predetermined wavelength selected from a plurality of predetermined wavelengths, from an input port to an output port is provided. The optical apparatus includes an interferometer coupled to the input and output ports. The interferometer includes first and second optical paths. Each wavelength component is split into a first wavelength component portion on the first path and a wavelength component second portion on the second path. A plurality of wavelength selective optical phase modulators is arranged in the first path and includes one optical phase modulator for each predetermined wavelength. Each modulator receives wavelength component first portions at a predetermined one wavelength. Each optical phase modulator is selectively operable to phase shift each corresponding wavelength component first portion by first or second predetermined phase shifts, whereby the corresponding wavelength component is or is not coupled from the input port to the output port.
In accordance with one aspect of the invention, a controller is coupled to each optical phase modulator and selects the first or said second predetermined phase shifts.
In accordance with another aspect of the invention, a de-multiplexer is disposed in the first path and couples each wavelength component from the first optical path to each corresponding one optical phase modulator.
In accordance with yet another aspect of the invention, a multiplexer is disposed in the first path and couples each optical wavelength component from each optical phase modulator to the first optical path.
In one embodiment of the invention, a multiplexer/de-multiplexer is disposed in the first path and couples each wavelength component between the first optical path.
In an embodiment of the invention, each corresponding one optical phase modulator and each optical phase modulator is a non-reciprocal phase shifter.
A method in accordance with the invention provides selective coupling of multiplexed wavelength components of optical signals comprising a plurality of multiplexed wavelength components from an input port to an output port. In accordance with the method the multiplexed wavelength components are coupled from the input port to an interferometer. Each wavelength component is split into a wavelength component first portion coupled onto a first optical path and a wavelength component second portion coupled onto a second optical path. A plurality of phase modulators is provided in the first path. Each wavelength component first portion is coupled to a corresponding one of said phase modulators. Each phase modulator is controlled individually to selectively subject each corresponding wavelength component first portion to a first or a second predetermined phase shift. Each wavelength component first portion is combined with each corresponding wavelength component second portion on a wavelength by wavelength basis to produce first or second interference states each having a predetermined relationship to the first or said second predetermined phase shift, whereby each wavelength component is coupled or is not coupled to the output port.
The method includes utilizing a controller to control each phase modulator. In accordance with one embodiment of the invention a step of utilizing a phase shifter for each said phase modulator is provided. In one particular embodiment, a non-reciprocal phase shifter is utilized for each phase modulator.
In accordance with one aspect of the invention, multiplexed wavelength components are separated into non-multiplexed wavelength components prior to coupling to a corresponding one of the phase modulators.